As elements for regulating the volume and the tone of audio electronic apparatuses are known devices in which analogue variable resistances are disposed separately for volume, low frequency tone, high frequency tone, volume ratio between left and right speakers, volume ratio between front and rear speakers etc. for the volume and tone control, and those in which a common electronic regulator is disposed for all the modes described above.
In the former, the volume or the tone is regulated by varying the rotational angle of the knob of a corresponding analogue variable resistance or the shift thereof. On the other hand, in the latter, the levels set for each of the modes is stored in a memory, referring to which the volume, the high and low frequency tone, the balance regulation of the left and right as well as the front and rear speakers, etc. are regulated electronically, and one of the set levels (digital value), which is selected by means of a mode selection switch, is changed by means of a volume up/down key.
FIG. 6 is a scheme showing the panel construction of such a prior art audio control device (where the parts which are not pertinent to this invention are omitted); FIG. 7 is a block diagram therefor; and FIG. 8 is a scheme for explaining the working mode of that device.
On the panel PNL are mounted mode selection switches Ka.about.Ke, each of them having a lamp, corresponding to the volume (VOL), the low frequency tone (BAS), the high frequency tone (TRE), the balance of left and right speakers (BAL) and the volume ratio of front and rear speakers (FAD), a level display LDP indicating the level set for the selected mode, a first and a second level regulation key LDK and LUK for regulating the level set for the selected mode. Further lamps La.about.Le constitute a mode display part MLP.
A control center unit CNT constituted by a microcomputer includes a processor CPU and a memory MEM, as indicated in FIG. 7 and in the memory MEM the level set for each of the modes is stored. The level set for each of the modes is inputted in an electronic regulator EVT, which generates a value of resistance corresponding to the set level.
Now, when a certain mode selection switch, e.g. the mode selection switch Ka for regulating the volume is pushd so that the volume mode (VOL mode) is selected, the processor CPU lightens the lamp Ka corresponding to the switch Ka, indicating that the volume mode has been selected and at the same time reads out the set volume level L from the memory MEM, which level is indicated in the level display LDP (see FIG. 8).
In this state, the level regulation key LUK is pushed, when it is desired to increase the volume, and the level regulation key LDK is pushed, when it is desired to decrease the volume. The processor CPU changes the volume level according to the following formula: EQU L+1.fwdarw.L,
until the level reaches the upper limit, every time when the level regulation key LUK is pushed, and the processor CPU changes the volume level according to the following formula: EQU L-1.fwdarw.L,
until the level reaches the lower limit, every time when the level regulation key LDK is pushed.
In addition, parallel to the procedure described above, the processor CPU controls continuously the value of resistance for the volume regulation of the electronic regulator EVL and at the same time lightens dislay elements L.sub.i (i=1, 2, . . . ) of the level display LDP under the level corresponding to that set in the manner described above. Further, also for the low frequency tone, the high frequency tone, the balance and the fader, a desired mode is selected similarly by pushing the corresponding mode selection key Ka.about.Ke and after that the level regulation can be effected therefor by pushing one of the level regulation keys LDK and LUK. However, for the balance mode (BAL mode), the level regulation key LDK acts so as to increase the volume ratio of the left channel to the right channel and the level regulation key LUK acts so as to increase the volume ratio of the right channel to the left channel. Furthermor, for the fader mode (FAD mode), the level regulation key LDK acts so as to increase the volume ratio of the rear speaker to the front speaker and the level regulation key LUK acts so as to increase the volume ratio of the front speaker to the rear speaker.
As mentioned above, the electronic regulator construction has an advantage that the number of variable resistances is reduced. However, on the other hand, according to the prior art electronic regulator construction, five key switches for the mode selection and two key swtiches for the level regulation and thus too many wires connecting these key switches with the processor are necessary, what gives rise to problems concerning the reduction in size of the audio electronic devices or other design, their fabrication and their cost.
Furthermor, in the prior art electronic regulator, since the up and down regulation of the set level is effected not by the rotation or the shift of the element for the operation (knob) as for the analogue variable resistances, but by pushing the key switches, no operational feeling, which the operator can have by the analogue variable resistances, cannot be obtained, what gives rise to a problem that the operability is not good.